1. Field of the Invention
The present invention relates to a detecting agent. More particularly, it pertains to a detecting agent for a hydride gas contained in a gas which is used for chemical vapor deposition (CVD), ion implantation or the like in a semiconductor menufacturing process and then discharged from the process.
2. Description of the Related Arts
With the development of semiconductor industries, there has recently been a steady rise in the amounts of inflammable hydride gases such as arsine, phosphine, silane, diborane and selenium hydride that are used in the above-mentioned industries.
These hydride gases are indispensable each as a raw material gas or a doping gas for the production process of silicon semiconductors and compound semiconductors, but they are highly toxic. It is therefore, necessary in the handling of any of the foregoing hydride gases, to determine at all times whether or not the gas leaks out to the working environment, and in the event of a gas leakage to notify the workers of the leakage without fail and simultaneously take appropriate safety measures thereagainst.
In addition, the exhaust gas discharged from a semiconductor manufacturing process frequently contains some of the aforesaid hydride gases and thus, it is required to purify the exhaust gas by the use of a detoxifying apparatus, and at the same time, to confirm the sufficient removal of the hydride gases prior to the discharge of the exhaust gas.
It is well-known that the use of a detecting agent is effective for detecting a hydride gas. As a method for using a detecting agent for example, in the case of detecting a leakage of the hydride gas into a working environment, mention may be made of a method in which a gas taken in the working environment is passed through a detector tube made of a glass tube packed inside with a detecting agent, and a leakage, if any, is detected by the discoloration (that is, color change, as referred to hereinafter) of the detecting agent. In the case of detecting the breakthrough of a harmful gas (hydride gas) in a purifying column for the harmful gas, there is generally adopted a detection method in which an observation is made for a discoloration of a detecting agent packed in an observation port of the purifying column.
There have heretofore been known for example, as a detecting agent for hydride gases, a detecting agent for phosphine which comprises a mercuric salt or a mercuric complex salt alone or a mixture of the same and a ferric salt or a cupric salt along with a silica-gel carrier supporting any of the aforesaid salt (refer to Japanese patent publication No. 844/1948); and a detecting agent for arsine and phosphine which comprises gold chloride and mercuric chloride that are supported on a granular carrier (refer to U.S. Pat. No. 3,112,998).
However, the above-mentioned detecting agents involve the problems that the sensitivity is not necessarily sufficient and that delicate care must be taken in handling mercury (II) and a salt thereof because of their extremely high toxicity.
Moreover, in the case where there is contained, in a gas which is the object of detection, hydrogen gas which is employed as a carrier gas in a semiconductor manufacturing process or the like or hydrogen gas which is formed by the catalytic cracking of a purifying agent and a hydride gas at the time of discharge, the detecting agent is discolored by the aforesaid hydrogen, thus causing the problem that selective detection only of the hydride gas is made impossible thereby.